Negative electrode active material for nonaqueous electrolyte secondary battery, nonaqueous electrolyte secondary battery, and battery pack

Abstract

A negative electrode active material for a nonaqueous electrolyte secondary battery of an embodiment includes a carbonaceous material, a silicon oxide phase in the carbonaceous material, and a silicon phase in the silicon oxide phase. The negative electrode active material has a crack in the carbonaceous material, and the longest side of the crack has a length equal to or greater than ⅕ of the diameter of the negative electrode active material.

What is claimed is: 
     
       1. A negative electrode active material for a nonaqueous electrolyte secondary battery, the negative electrode active material comprising:
 a carbonaceous material; 
 a silicon oxide phase in the carbonaceous material; and 
 a silicon phase in the silicon oxide phase, wherein 
 the negative electrode active material has a crack having a first end in the carbonaceous material including the silicon oxide phase, and a side of the crack has a length L equal to or greater than ⅕ of a diameter D1 of the negative electrode active material, and 
 the crack includes a second end that is opened to an outer surface of-the carbonaceous material including the silicon oxide phase, 
 wherein the silicon phase is covered by the silicon oxide phase, and 
 wherein the silicon oxide phase is covered by the carbonaceous material having the crack. 
 
     
     
       2. The material according to  claim 1 , wherein where a mass of the carbonaceous material is WC, a mass of the silicon oxide phase is WSiO and a mass of the silicon phase is WSi, WC, WSiO and WSi satisfy 0.85<[WSiO+WSi]/[WC+WSiO+WSi]≦0.95. 
     
     
       3. The material according to  claim 1 , wherein the negative electrode active material has a crack in the carbonaceous material, and a ratio (L/D) of the longest side L to a diameter D of the crack is 10 or more. 
     
     
       4. The material according to  claim 1 , wherein the porosity of the negative electrode active material is 5% or more to 25% or less. 
     
     
       5. A nonaqueous electrolyte secondary battery comprising: a negative electrode containing a negative electrode active material; a positive electrode containing a positive electrode active material; and a nonaqueous electrolyte, the negative electrode active material comprising:
 a carbonaceous material; 
 a silicon oxide phase in the carbonaceous material; and 
 a silicon phase in the silicon oxide phase, wherein 
 the negative electrode active material has a crack having a first end in the carbonaceous material including the silicon oxide phase, and a side of the crack has a length L equal to or greater than ⅕ of a diameter D of the negative electrode active material, and 
 the crack includes a second end that is opened to an outer surface of the carbonaceous material including the silicon oxide phase, 
 wherein the silicon phase is covered by the silicon oxide phase, and 
 wherein the silicon oxide phase is covered by the carbonaceous material having the crack. 
 
     
     
       6. The battery according to  claim 5 , wherein where a mass of the carbonaceous material is WC, a mass of the silicon oxide phase is WSiO and a mass of the silicon phase is WSi, WC, WSiO and WSi satisfy 0.85<[WSiO+WSi]/[WC+WSiO+WSi]≦0.95. 
     
     
       7. The battery according to  claim 5 , wherein the negative electrode active material has a crack in the carbonaceous material, and a ratio (L/D) of the longest side L to a diameter D of the crack is 10 or more. 
     
     
       8. The battery according to  claim 5 , wherein the porosity of the negative electrode active material is 5% or more to 25% or less. 
     
     
       9. A battery pack which uses a nonaqueous electrolyte secondary battery comprising: a negative electrode containing a negative electrode active material; a positive electrode containing a positive electrode active material; and a nonaqueous electrolyte, the negative electrode active material comprising:
 a carbonaceous material; 
 a silicon oxide phase in the carbonaceous material; and 
 a silicon phase in the silicon oxide phase, wherein 
 the negative electrode active material has a crack including a first end in the carbonaceous material including the silicon oxide phase, and a side of the crack has a length L equal to or greater than ⅕ of a diameter D of the negative electrode active material, and 
 the crack includes a second end that is opened to an outer surface of the carbonaceous material including the silicon oxide phase, 
 wherein the silicon phase is covered by the silicon oxide phase, and 
 wherein the silicon oxide phase is covered by the carbonaceous material having the crack. 
 
     
     
       10. The battery pack according to  claim 9 , wherein where a mass of the carbonaceous material is WC, a mass of the silicon oxide phase is WSiO and a mass of the silicon phase is WSi, WC, WSiO and WSi satisfy 0.85<[WSiO+WSi]/[WC+WSiO+WSi]≦0.95. 
     
     
       11. The battery pack according to  claim 9 , wherein the negative electrode active material has a crack in the carbonaceous material, and a ratio (L/D) of the longest side L to the diameter D of the crack is 10 or more. 
     
     
       12. The battery pack according to  claim 9 , wherein the porosity of the negative electrode active material is 5% or more to 25% or less. 
     
     
       13. The material according to  claim 1 , wherein the carbonaceous material includes graphite. 
     
     
       14. The battery according to  claim 5 , wherein the carbonaceous material includes graphite. 
     
     
       15. The battery pack according to  claim 9 , wherein the carbonaceous material includes graphite. 
     
     
       16. The material according to  claim 1 , wherein the negative electrode active material are particles, and
 the outer surface of the carbonaceous material including the silicon oxide phase is an outer surface of the particles being the negative electrode active material. 
 
     
     
       17. The battery according to  claim 5 , wherein the negative electrode active material are particles, and
 the outer surface of the carbonaceous material including the silicon oxide phase is an outer surface of the particles being the negative electrode active material. 
 
     
     
       18. The battery pack according to  claim 9 , wherein the negative electrode active material are particles, and wherein
 the outer surface of the carbonaceous material includes the silicon oxide phase is an outer surface of the particles being the negative electrode active material.